Granulomatous inflammation in ginbuna crucian carp Carassius auratus langsdorfii against Mycobacterium gordonae

In this study, we investigated the immune responses against Mycobacterium gordonae in ginbuna crucian carp. Cumulative mortality of ginbuna injected with 2.0 × 107 CFU of M. gordonae was 50% at 170 days post-infection. CD4-1, CD8α, T-bet and IFNγ2 gene expression levels were significantly upregulated in ginbuna injected with 1.9 × 108 CFU of M. gordonae at 21 and 28 days post-infection. The CD4-2 level did not change during the experiment. Granulomatous responses consisted of central macrophage accumulation and surrounding lymphocytes, and Ziehl-Neelsen-positive bacteria were observed in the trunk kidney of the challenged fish. Immunohistochemistry using anti-ginbuna IFNγs and anti-ginbuna CD4-1 polyclonal antibody revealed that the marginal lymphocytes were positive for CD4-1, and the IFNγ-producing cells surrounded the mycobacterial cell-laden phagocytes. These results suggest that CD4-1+ cells and IFNγ2 play important roles in the granulomatous inflammation against Mycobacterial infections in teleosts.